The present disclosure generally relates to curable phase change compositions and their use in methods for protecting images on a substrate.
The electrostatographic process, and particularly the xerographic process, is well known. This process involves the formation of an electrostatic latent image on a photoreceptor, followed by development of the image with a developer, and subsequent transfer of the image to a suitable substrate. In xerography, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. The radiation selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image on the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles, called toner, on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a recording medium, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
Known methods of protecting images include adding wax to the toner and applying an overprint coating over the image on the substrate. The overprint coating, often referred to as an overprint varnish or composition, is typically a liquid film coating that may be dried and/or cured. Curing may be accomplished through drying or heating or by applying ultraviolet light or low voltage electron beams to polymerize (crosslink) the components of the overcoat. However, known overprint coatings, such as those described in U.S. Pat. Nos. 4,070,262, 4,071,425, 4,072,592, 4,072,770, 4,133,909, 5,162,389, 5,800,884, 4,265,976, and 5,219,641, for example, fail to adequately protect toner-based prints and do not possess the requisite properties for controlled application, such as, for example, by an ink jet printer.
Typically, known coating formulations are applied using a liquid film coating device, and thus are often applied over the entire surface of the image, i.e., flood coating. Applying a composition to part of an image, i.e., spot coating, is possible, but it requires preparing a plate or cylinder prior to application of the overprint composition. Thus, applying known coating formulations can be inefficient, difficult, and time-consuming and is not desirable for integration with variable-data digital printing.
A need exists for an overprint composition, particularly one that can be applied by ink jet printing, that provides increased heat and abrasion resistance, especially for stress case media, such as flexible packaging and automobile owner manuals.